For at least the last 15 years, there have been several configurations of “under-sink” reverse osmosis (RO) systems designed to improve the quality of a relatively small amount of water to be used for drinking and cooking by a homeowner. A few examples of such systems are described in U.S. Pat. Nos. 4,650,586 and 4,629,568 both of which are owned by the assignee of the present invention and incorporated herein by reference.
An objective of typical under sink reverse osmosis systems is to decrease the total dissolved solids (TDS) of the supplied city or well water and thereby improve the taste, odor or chemical makeup of the water. These under the sink reverse osmosis systems can be upgraded to include additional unit processes to pre-treat the incoming water for chlorine or sediment removal prior to the RO unit. This pre-treatment improves the operation and prolongs the life of the RO membrane. In addition pre-treatment further polishes the water produced by the RO membrane to remove both trace organics that might cause taste issues and small molecular weight contaminants that might pass through or be poorly rejected by the RO membrane. Therefore today there are many versions of RO units that effectively remove or reduce specific unwanted ionic contaminants and or organics to improve the quality of the water for the use of the homeowner.
There is increasing concern that some of the water supplies, both from wells, surface waters or even municipalities may, from time to time contain unwanted microbiological contaminants such as pathogens, that may be harmful when ingested by people, especially persons with immune system deficiencies.
While the pore size of the common RO membrane is sufficiently small to prevent the passing of microbiological contaminants, testing over the years has shown that the RO unit alone cannot consistently meet the relatively stringent requirements to be classified a “microbiological purifier” as defined in EPA in the “Guide Standard and Protocol for Testing Microbiological Water Purifiers” (1987 revision). It is believed that the reason for this is the imperfections in the RO membrane itself or in the methods of bonding the membrane together at the ends of the assemblies. While there are several methods available to deal with such concerns, such as boiling the water for several minutes or adding anti-pathogen agents like iodine to the water, most of these are not convenient and/or may make the water less pleasant to drink. Ultraviolet light filters that neutralize contaminants by exposure to certain wavelengths of light are also known in the art. These filters suffer from several practical drawbacks including the fact that they rely on electricity to function and also require relatively complex controls to ensure that water is not overheated due to extended exposure to the light.